headless: Add support for host resolver mapping

headless/public/headless_browser.cc

Index: headless/public/headless_browser.cc
diff --git a/headless/public/headless_browser.cc b/headless/public/headless_browser.cc
index 9f166b40a7033ad863b01e23e0a653311a3b7b82..95fe8b69fca9b2daf504bb7ce3dbaf1814bdd8a2 100644
--- a/headless/public/headless_browser.cc
+++ b/headless/public/headless_browser.cc
@@ -58,6 +58,11 @@ Builder& Builder::SetSingleProcessMode(bool single_process_mode) {
   return *this;
 }
 
+Builder& Builder::SetHostResolverRules(const std::string& host_resolver_rules) {
+  options_.host_resolver_rules = host_resolver_rules;
+  return *this;
+}
+
 Options Builder::Build() {
   return options_;
 }